SoftLayer/IBM provider is broken

## Summary

Can't obtain a driver for SOFTLAYER provider

## Detailed Information

I'm using Python 3.9/3.10 and apache-libcloud==3.8.0
When trying to get driver for the SOFTLAYER provider the following error obtained:

```
from libcloud.compute.types import Provider
from libcloud.compute.providers import get_driver
cls = get_driver(Provider.SOFTLAYER)
File "/usr/local/lib/python3.10/enum.py", line 437, in __getattr__
raise AttributeError(name) from None
AttributeError: SOFTLAYER
```

I tried to debug it and noticed that the cls object doesn't include the SOFTLAYER member. It includes the IBM instead. But when I try to use the Provider.IBM, the following exception is displayed:
`Exception: Provider no longer supported: http://www.ibm.com/midmarket/us/en/article_cloud6_1310.html, please visit: IBM SmartCloud Enterprise has been deprecated in favour of IBM SoftLayer Public Cloud, please use the SOFTLAYER provider.`

Reproduce the error using the libcloud.compute.types.Provider and libcloud.compute.providers.get_driver imports shown in the report. Trace how the SoftLayer and IBM provider entries are defined and selected; done means Provider.SOFTLAYER can be obtained and no longer leads to the deprecated IBM provider error.

Scritto dal modello di indicizzazione a partire dal testo della issue.